[Mesa-dev] [PATCH 1/3] i965/fs: Implement the WaCMPInstFlagDepClearedEarly work-around.

[Matt Turner]

Prevents piglit regressions from the next patch.
---
 src/mesa/drivers/dri/i965/brw_fs_generator.cpp | 37 +++++++++++++++++++++++++-
 1 file changed, 36 insertions(+), 1 deletion(-)

diff --git a/src/mesa/drivers/dri/i965/brw_fs_generator.cpp b/src/mesa/drivers/dri/i965/brw_fs_generator.cpp
index 77d4908..8cd36f8 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_generator.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_generator.cpp
@@ -1734,7 +1734,42 @@ fs_generator::generate_code(const cfg_t *cfg, int dispatch_width)
          brw_F16TO32(p, dst, src[0]);
          break;
       case BRW_OPCODE_CMP:
-	 brw_CMP(p, dst, inst->conditional_mod, src[0], src[1]);
+         /* The Ivybridge/BayTrail WaCMPInstFlagDepClearedEarly workaround says
+          * that when the destination is a GRF that the dependency-clear bit on
+          * the flag register is cleared early.
+          *
+          * Suggested workarounds are to disable coissuing CMP instructions
+          * or to split CMP(16) instructions into two CMP(8) instructions.
+          *
+          * We choose to split into CMP(8) instructions since disabling
+          * coissuing would affect CMP instructions not otherwise affected by
+          * the errata.
+          */
+         if (dispatch_width == 16 && brw->gen == 7 && !brw->is_haswell) {
+            if (dst.file == BRW_GENERAL_REGISTER_FILE) {
+               brw_set_default_compression_control(p, BRW_COMPRESSION_NONE);
+               brw_CMP(p, firsthalf(dst), inst->conditional_mod,
+                          firsthalf(src[0]), firsthalf(src[1]));
+               brw_set_default_compression_control(p, BRW_COMPRESSION_2NDHALF);
+               brw_CMP(p, sechalf(dst), inst->conditional_mod,
+                          sechalf(src[0]), sechalf(src[1]));
+               brw_set_default_compression_control(p, BRW_COMPRESSION_COMPRESSED);
+
+               multiple_instructions_emitted = true;
+            } else if (dst.file == BRW_ARCHITECTURE_REGISTER_FILE) {
+               /* For unknown reasons, the aforementioned workaround is not
+                * sufficient. Overriding the type when the destination is the
+                * null register is necessary but not sufficient by itself.
+                */
+               assert(dst.nr == BRW_ARF_NULL);
+               dst.type = BRW_REGISTER_TYPE_D;
+               brw_CMP(p, dst, inst->conditional_mod, src[0], src[1]);
+            } else {
+               unreachable("not reached");
+            }
+         } else {
+            brw_CMP(p, dst, inst->conditional_mod, src[0], src[1]);
+         }
 	 break;
       case BRW_OPCODE_SEL:
 	 brw_SEL(p, dst, src[0], src[1]);
-- 
2.0.4